The field of this invention is microfluidic manipulation of fluids and ions.
Microfluidics is revolutionizing the way activities are performed in a substantial proportion of chemical and physical operations. One area of microfluidics is the manipulation of small volumes of liquids or liquid compositions on a solid substrate, where a network of channels and reservoirs are present. By employing electric fields with electrically conducting liquids, volumes and/or ions can be moved from one site to another, different solutions formed by mixing liquids and/or ions, reactions performed, separations performed, and analyses carried out. In fact, in common parlance, the system has been referred to as xe2x80x9ca laboratory on a chip.xe2x80x9d Various prior art devices of this type include U.S. Pat. Nos. 6,010,608, 6,010,607, 6,001,229, 5,858,195, 5,858,187 and PCT application No. 96/0547 are a family of applications concerned with injection of sample solutions. See also, U.S. Pat. No. 5,599,432, EPA 0620432, and Verheggen et al., J. of Chromatography 452 (1988) 615-622.
In many of the operations, there is an interest in producing a sharply defined volume of ions as a plug, where the boundaries for specified ions or groups of ions are sharp and either linear or only slightly bowed. At the same time, it may be desired to inject a sample having a well-defined volume. Alternatively, it may be desired to prestack the components in a multicomponent sample, e.g., to improve electrophoretic separation of the components of the sample. In still other applications, it is desired to concentrate sample components present in a sample, prior to injecting the sample for analysis, e.g., by electrophoresis separation.
It is a general objective of the present invention to provide a microfluidics device and system that can be controlled to achieve these various desired sample-injection features. The invention includes, in one aspect, a method of injecting a liquid sample into an electrolyte channel in a microfluidics device having a channel network that includes an electrolyte channel having upstream and downstream channel portions and first, second, and third side channels that intersect the electrolyte channel between the two channel portions at first, second, and third ports, respectively, where at least one of the ports is axially spaced along the electrolyte channel from the other two ports.
The method includes the steps of (a) supplying a sample to the first side channel, (b) applying across the first side channel and at least one of the other two side channels, a voltage potential effective to move sample in the first channel into a volume element of the electrolyte chamber extending between the first and at least one other port which is axially offset from the first port, (c) simultaneously controlling the voltage applied to the three side channels, and, optionally, one or both of the upstream and downstream channel end portions, to create a sample volume element in the electrolyte channel that has a desired leading- and trailing-edge shape and/or distribution of sample components within the volume elements, and (d) simultaneously controlling the voltage applied to the upstream and downstream channel portion, and to at least two of the side channels, to advance the sample element having a desired leading- and trailing-edge shape and/or distribution of sample components in a downstream direction within the electrolyte channel.
For use in injecting a sample containing a plurality of sample components in a volume element having a substantially uniform distribution of the sample components, the first port is axially disposed between the second and third ports, applying step (b) is effective to move sample in the first channel into a volume element of the electrolyte chamber extending between the second and third ports, and controlling step (c) is effective to move an electrolyte solution from the upstream channel portion through the second port and an electrolyte solution from the downstream portion through the third port, thus to sharpen the upstream and downstream boundaries of the sample volume.
The first port may be axially aligned with the second port, or axially spaced from both the second the third ports. The controlling step (d) is effective to move an electrolyte solution in the upstream channel portion successively through the second, first and third ports, to move sample contained in the three side channels away from the electrolyte channel.
In another embodiment, the method is used for injecting a sample containing a plurality of sample components in a volume element, and prestacking the sample components within the volume element according to their electrophoretic mobilities, where the sample contains a plurality of components with different electrophoretic mobilities and one of a leading-edge ion having an electrophoretic mobility greater than that of said sample components or a trailing-edge ion having an electrophoretic mobility less than that of said sample components. In this method, the first port is axially disposed between the second and third ports, applying step (b) is effective to move sample in the first channel into a volume element of the electrolyte chamber extending between the second and third ports, controlling step (c) is effective to move an electrolyte solution from the upstream channel portion through the second port and an electrolyte solution from the downstream portion through the third port, thus to sharpen the upstream and downstream boundaries of the sample volume, where the electrolyte solution in both the upstream and downstream portions includes the other of the leading-edge or trailing-edge ions, and controlling step (d) is initially effective in stacking the sample components in the sample volume in accordance with their electrophoretic mobilities, by isotachophoretic separation.
As above, the first port may be axially aligned with the second port, or axially spaced from both the second the third ports. The controlling step (d) is effective to move an electrolyte solution in the upstream channel portion successively through the second, first and third ports, to move sample contained in the three side channels away from the electrolyte channel.
Alternatively, for prestacking the sample components, the second port is axially disposed between the first and third ports, applying step (b) is effective to move sample in the first channel into a volume element of the electrolyte chamber extending between the first and second ports, controlling step (c) is effective to move a solution containing one of a leading-edge ion having an electrophoretic mobility greater than that of said sample components or a trailing-edge (terminating) ion having an electrophoretic mobility less than that of said sample components from the third channel into the second channel, and controlling step (d) is initially effective in stacking the sample components in the sample volume in accordance with their electrophoretic mobilities, by isotachophoretic separation. The other of the leading- or trailing-edge ion is contained in the upstream and downstream portions of the electrolyte channel.
In another embodiment for injecting a sample containing one or more sample components, and concentrating the component(s) at the upstream or downstream side of the sample volume, the first, second, and third ports are axially spaced from one another, and the second port is disposed between the first and third ports. Applying step (b) includes applying a DC voltage potential across the first and second side channels, to move sample in the first channel into a volume element of the electrolyte chamber extending between the first and second ports, and controlling step (c) includes applying an AC voltage between the third side channel and an upstream or downstream channel portion, where the first and second ports are disposed between and spaced from the third side channel and channel portion to which the AC voltage is applied, thereby to concentrate sample components in the sample volume at an end of the sample volume adjacent the channel portion to which the AC voltage is applied.
In still another embodiment for concentrating sample components, the first and third channels are axially aligned or nearly so on opposite sides of the electrolyte channel, the second channel is axially spaced from the first and third channels, applying step (b) includes applying a DC voltage potential across the first and second side channels, to move sample in the first channel into a volume element of the electrolyte chamber extending between the first and second ports, and controlling step (c) includes applying an AC voltage between the third channel and the adjacent upstream or downstream channel end portion between the third side channel and an upstream or downstream channel portion, thereby to concentrate sample components in the sample volume at an end of the sample volume adjacent the channel portion to which the AC voltage is applied.
Forming another aspect of the invention is a microfluidic system designed for use in injecting a defined-volume liquid sample into a capillary electrolyte channel, for transport through the channel. The device includes (a) a microfluidic device having a channel network that includes such an electrolyte channel having upstream and downstream channel portions and first, second, and third side channels that intersect the electrolyte channel between the two channel portions at first, second, and third ports, respectively, where at least one of the ports is axially spaced along the electrolyte channel from the other two ports, (b) ports for supplying liquid medium to the electrolyte channel and the side channels, and (c) upstream and downstream electrodes, and first, second, and third electrodes adapted to communicate with liquid medium contained in upstream and downstream portions of the electrolyte channel, and the first, second, and third side channels, respectively, and
A voltage controller (d) operatively connected to the upstream downstream, and first, second, and third electrodes, for: (i) applying across the first side channel and at least one of the other two side channels, a voltage potential effective to move a liquid sample contained in the first channel into a volume element of the electrolyte chamber extending between the first and at least one other port which is axially offset from the first port, (ii) simultaneously controlling the voltage applied to the three side channels, and at least one of said upstream and downstream channel end portions, to create a sample volume element in the electrolyte channel that has a desired leading and trailing-edge shape and/or distribution of sample components within the volume elements, and (iii) simultaneously controlling the voltage applied to the upstream and downstream channel portion, and to at least two of the side channels, to advance the sample element having a desired leading- and trailing-edge shape and/or distribution of sample components in a downstream direction within the electrolyte channel.
The device has the structural and controlled-voltage features described above.
These and other objects of the invention will become more fully apparent when the following detailed description of the invention is read in conjunction with the accompanying drawings.